1. Field of the Invention
The present invention relates to an orthogonal complex spreading method for a multichannel and an apparatus thereof, and in particular, to an improved orthogonal complex spreading method for a multichannel and an apparatus thereof which are capable of decreasing a peak power-to-average power ratio by introducing an orthogonal complex spreading structure and spreading the same using a spreading code, implementing a structure capable of spreading complex output signals using a spreading code by adapting a permutated orthogonal complex spreading structure for a complex-type multichannel input signal with respect to the summed values, and decreasing a phase dependency of an interference based on a multipath component (when there is one chip difference) of a self signal, which is a problem that is not overcome by a permutated complex spreading modulation method, by a combination of an orthogonal Hadamard sequence.
2. Description of the Conventional Art
Generally, in the mobile communication system, it is known that a linear distortion and non-linear distortion affect power amplifier. The statistical characteristic of a peak power-to-average power ratio has a predetermined interrelationship for a non-linear distortion.
The third non-linear distortion which is one of the factors affecting the power amplifier causes an inter-modulation product problem in an adjacent frequency channel. The above-described inter-modulation product problem is generated due to a high peak amplitude for thereby increasing an adjacent channel power (ACP), so that there is a predetermined limit for selecting an amplifier. In particular, the CDMA (Code Division Multiple Access) system requires a very strict condition with respect to a linearity of a power amplifier. Therefore, the above-described condition is a very important factor.
In accordance with IS-97 and IS-98, the FCC stipulates a condition on the adjacent channel power (ACP). In order to satisfy the above-described condition, a bias of a RF power amplifier should be limited.
According to the current IMT-2000 system standard recommendation, a plurality of CDMA channels are recommended. In the case that a plurality of channels are provided, the peak power-to-average power ratio is considered as an important factor for thereby increasing efficiency of the modulation method.
The IMT-2000 which is known as the third generation mobile communication system has a great attention from people as the next generation communication system following the digital cellular system, personal communication system, etc. The IMT-2000 will be commercially available as one of the next generation wireless communication system which has a high capacity and better performance for thereby introducing various services and international loaming services, etc.
Many countries propose various IMT-2000 systems which IC require high data transmission rates adapted for an internet service or an electronic commercial activity. This is directly related to the power efficiency of a RF amplifier.
The CDMA based IMT-2000 system modulation method introduced by many countries is classified into a pilot channel method and a pilot symbol method. Of which, the former is directed to the ETRI 1.0 version introduced in Korea and is directed to CDMA ONE introduced in North America, and the latter is directed to the NTT-DOCOMO and ARIB introduced in Japan and is directed to the FMA2 proposal in a reverse direction introduced in Europe.
Since the pilot symbol method has a single channel effect based on the power efficiency, it is superior compared to the pilot channel method which is a multichannel method. However since the accuracy of the channel estimation is determined by the power control, the above description does not have its logical ground.
FIG. 1 illustrates a conventional complex spreading method based on a CDMA ONE method. As shown therein, the signals from a fundamental channel, a supplemental channel, and a control channel are multiplied by a Walsh code by each multiplier of a multiplication unit 20 through a signal mapping unit 10. The signals which are multiplied by a pilot signal and the Walsh signal and then spread are multiplied by channel gains A0, A1, A2 and A3 by a channel gain multiplication unit 30.
In a summing unit 40, the pilot signal multiplied by the channel gain A0 and the fundamental channel signal multiplied by the channel gain A1 are summed by a first adder for thereby obtaining an identical phase information, and the supplemental channel signal multiplied by the channel gain A2 and the control channel signal multiplied by the channel gain A3 are summed by a second adder for thereby obtaining an orthogonal phase information.
The thusly obtained in-phase information and quadrature-phase information are multiplied by a PN1 code and PN2 code by a spreading unit 50, and the identical phase information multiplied by the PN2 code is subtracted from the identical phase information multiplied by the PN1 code and is outputted as an I channel signal, and the quadrature-phase information multiplied by the PN1 code and the in-phase information multiplied by the PN2 code are summed and are outputted through a delay unit as a Q channel signal.
The CDMA ONE is implemented using a complex spreading method. The pilot channel and the fundamental channel spread to a Walsh code 1 are summed for thereby forming an in-phase information, and the supplemental channel spread to the Walsh code 2 and the control channel spread to a Walsh code 3 are summed for thereby forming an quadrature-phase information. In addition, the in-phase information and quadrature-phase information are complex-spread by PN codes.
FIG. 2A is a view illustrating a conventional CDMA ONE method, and FIG. 2B is a view illustrating a maximum eye-opening point after the actual shaping filter of FIG. 2A.
As shown therein, in the CDMA ONE, the left and right information, namely, the in-phase information (I channel) and the upper and lower information, namely, the quadrature-phase information (Q channel) pass through the actual pulse shaping filter for thereby causing a peak power, and in the ETRI version 1.0 shown in FIGS. 3A and 3B, a peak power may occur in the transverse direction for thereby causing deterioration.
In view of the crest factor and the statistical distribution of the power amplitude, in the CDMA ONE, the peak power is generated in vertical direction, so that the irregularity problem of the spreading code and an inter-interference problem occur.
Accordingly, it is an object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof overcome the aforementioned problems encountered in the conventional art.
The CDMA system requires a strict condition for a linearity of a power amplifier, so that the peak power-to-average power ratio is important. In particular, the characteristic of the IMT-2000 system is determined based on the efficiency of the modulation method since multiple channels are provided, and the peak power-to-average power ratio is adapted as an important factor.
It is another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof which have an excellent power efficiency compared to the CDMA-ONE introduced in U.S.A. and the W-CDMA introduced in Japan and Europe and is capable of resolving a power unbalance problem of an in-phase channel and a quadrature-phase channel as well as the complex spreading method.
It is still another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof which is capable of stably maintaining a low peak power-to-average power ratio.
It is still another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof in which a spreading operation is implemented by multiplying a predetermined channel data among data of a multichannel by an orthogonal Hadamard sequence and a gain and, multiplying a data of another channel by an orthogonal Hadamard sequence and a gain, summing the information of two channels in complex type, multiplying the summed information of the complex type by the orthogonal Hadamard sequence of the orthogonal type, obtaining a complex type, summing a plurality of channel information of the complex type in the above-described manner and multiplying the information of the complex type of the multichannel by a spreading code sequence.
It is still another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof which is capable of decreasing the probability that the power becomes a zero state by preventing the FIR filter input state from exceeding xc2x190xc2x0 in an earlier sample state, increasing the power efficiency, decreasing the consumption of a bias power for a back-off of the power amplifier and saving the power of a battery.
It is still another object of the present invention to provide an orthogonal complex spreading method for a multichannel and an apparatus thereof which is capable of implementing a POCQPSK (Permutated Orthogonal Complex QPSK) which is another modulation method and has a power efficiency similar with the OCQPSK (Orthogonal Complex QPSK).
In order to achieve the above objects, there is provided an orthogonal complex spreading method for a multichannel which includes the steps of complex-summing xcex1n1WM,n1Xn1 which is obtained by multiplying an orthogonal Hadamard sequence WM,n1 by a first data Xn1 of a n-th block and xcex1n2WM,n2Xn2 which is obtained by multiplying an orthogonal Hadamard sequence WM,n2 by a second data Xn2 of a n-th block; complex-multiplying xcex1n1WM,n1Xn1+jxcex1n2WM,n2Xn2 which is summed in the complex type and WM,n3+jWM,n4 of the complex type using a complex multiplier and outputting as an in-phase information and quadrature-phase information; and summing only in-phase information outputted from a plurality of blocks and only quadrature-phase information outputted therefrom and spreading the same using a spreading code.
In order to achieve the above objects, there is provided an orthogonal complex spreading apparatus according to a first embodiment of the present invention which includes a plurality of complex multiplication blocks for distributing the data of the multichannel and complex-multiplying xcex1n1WM,n1Xn1+jxcex1n2WM,n2Xn2 in which xcex1n1WM,n1Xn1 which is obtained by multiplying the orthogonal Hadamard sequence WM,n1 with the first data Xn1 of the n-th block and the gain xcex1n1 and xcex1n2WM,n2Xn2 which is obtained by multiplying the orthogonal Hadamard sequence WM,n2 with the second data Xn2 of the n-th block and the gain xcex1n2 and WM,n3+WM,n4 using the complex multiplier; a summing unit for summing only the in-phase information outputted from each block of the plurality of the complex multiplication blocks and summing only the quadrature-phase information; and a spreading unit for multiplying the in-phase information and the quadrature-phase information summed by the summing unit with the spreading code and outputting an I channel and a Q channel.
In order to achieve the above objects, there is provided an orthogonal complex spreading apparatus according to a second embodiment of the present invention which includes first and second Hadamard sequence multipliers for allocating the multichannel to a predetermined number of channels, splitting the same into two groups and outputting xcex1n1WM,n1Xn1 which is obtained by multiplying the data Xn1 of each channel by the gain xcex1n1 and the orthogonal Hadamard sequence WM,n1;
a first adder for outputting       ∑          n      =      1        K    ⁢      xe2x80x83    ⁢      (                  α        n1            ⁢              W                  M          ,          n1                    ⁢              X        n1              )  
xe2x80x83which is obtained by summing the output signals from the first Hadamard sequence multiplier;
a second adder for outputting       ∑          n      =      1        K    ⁢      xe2x80x83    ⁢      (                  α        n2            ⁢              W                  M          ,          n2                    ⁢              X        n2              )  
xe2x80x83which is obtained by summing the output signals from the second Hadamard sequence multiplier; a complex multiplier for receiving the output signal from the first adder and the output signal from the second adder in the complex form of       ∑          n      =      1        K    ⁢      xe2x80x83    ⁢      (                            α          n1                ⁢                  W                      M            ,            n1                          ⁢                  X          n1                    +              j        ⁢                  xe2x80x83                ⁢                  α          n2                ⁢                  W                      M            ,            n2                          ⁢                  X          n2                      )  
xe2x80x83and complex-multiplying WM,I+jPWM,Q which n=1 consist of the orthogonal Hadamard code WM,I, and the permutated orthogonal Hadamard code PWM,Q that WM,Q and a predetermined sequence P are complex-multiplied; a spreading unit for multiplying the output signal from the complex multiplier by the spreading code; a filter for filtering the output signal from the spreading unit; and a modulator for multiplying and modulating the modulation carrier wave, summing the in-phase signal and the quadrature-phase signal and outputting a modulation signal of the real number.
Additional advantages, objects and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.